function changesrc(obj){
    var big_src = document.getElementById('big');
    big_src.src = obj.src.replace('50_','');
}
function plus(id){

    var number = document.getElementById('number'+id);
    number.value = parseInt(number.value) + 1;
    var total = document.getElementById('total'+id);
    var price = document.getElementById('price'+id);
    total.innerHTML = number.value * price.innerHTML;


}

function minus(id){
    var number = document.getElementById('number'+id);
    number.value = parseInt(number.value) - 1;
    if(number.value < 1){
        number.value = 1;
    }
    var total = document.getElementById('total'+id);
    var price = document.getElementById('price'+id);
    total.innerHTML = number.value * price.innerHTML;
}

function change_num(id){

    var price = document.getElementById('price'+id);
    var number = document.getElementById('number'+id);
    var total = document.getElementById('total'+id);
    if(number.value < 1){
        number.value = 1;
    }
    total.innerHTML = number.value * price.innerHTML;
}

function change_background(id){
    alert(id);
    var center1 = document.getElementById('center1');
    var center2 = document.getElementById('center2');
    var center3 = document.getElementById('center3');
    var center4 = document.getElementById('center4');

}
